This invention relates generally to brush wear detectors for dynamoelectric machines and more particularly to a brush wear detector utilizing light energy conductors, commonly called fiber optics, to complete or interrupt a light path to signal the existence of a worn brush condition.
Dynamoelectric machines, such as direct current (D.C.) motors, use carbon brushes to transfer power between an external source of electric power and a rotating commutator associated with the rotor of the D.C. motor. Since the brushes are in contact with the commutator, they must be periodically replaced after a predetermined amount of wear to assure adequate current conduction and to prevent damage to the commutator. Alternating current machines may similarly employ brushes and slip rings for the transfer of electric power and have similar brush wear problems.
A variety of brush wear detectors or indicators are known for signalling the need for brush replacement. Typically, such apparatus includes electrical circuitry whose operation is dependent upon the condition of wear as sensed by the movement of a self-winding brush follower spring which applies a biasing force against the rear end of the brush and whose other end is in contact with the commutator or slip rings of a dynamoelectric machine. When the brush is in a new or usable condition, the coil of the spring is in a first position away from the commutator. As the brush wears, however, it eventually reaches a second position near the commutator. This movement is utilized to open or close a set of electrical contacts which thereby energizes or deenergizes an electrical circuit for signalling the need for brush replacement. Examples of such apparatus include the brush wear detectors disclosed in: U.S. Pat. No. 4,488,078, entitled, "Brush Wear Detector", issued to Ronald C. Orton on Dec. 11, 1984; U.S. Pat. No. 4,344,009, entitled, "Brush Wear Indicator For A Dynamoelectric Machine Brush", issued to Kenneth R. Reynolds on Aug. 10, 1982; and U.S. Pat. No. 4,348,608, entitled, "Brush Wear Indicator", issued to Richard N. Michael on Sept. 7, 1982.
A second well known type of detector system employs an electrical conductor embedded within the brush. When the brush wears by a predetermined amount, the conductor contacts the commutator (or slip ring) which may serve to complete an electric circuit or, as by wearing through a loop at the end of the conductor, break an existing circuit. In either case, a worn brush condition is indicated. These embedded conductor systems suffer from the two primary deficiencies of having an electrical current carrying member in the current carrying brush and, since the conductor is usually metallic, of a metal to metal contact with the commutator.
Accordingly, it is an object of the present invention to provide an improvement in brush wear detectors for dynamoelectric machines.
It is a further object of the invention to detect a worn brush in a dynamoelectric machine using light energy.
It is another object of the invention to provide a brush wear detector for electrical machinery such as direct current motors.
It is yet a further object of the invention to provide a brush wear detector which utilizes electrically non-conductive fiber optics to thus preclude the use of electrically conductive wires associated with other types of wear detectors, near the voltages inherently present in the brush assemblies of dynamoelectric machines.